ZEFF ACCORDING TO THE SCHWINGER MULTICHANNEL METHOD IN POSITRON SCATTERING

We use the wave function from the Schwinger multichannel method to calculate Z(eff)-an annihilation parameter of positron-atom (or molecule) scattering. These Z(eff) are evaluated from the (N+1)-particle wave function and are calculated in a fully ab initio way (in a quantum chemistry sense). Our first applications are for positron scattering against He atoms and H-2 molecules. Our results for both systems are in excellent agreement with experimental data at thermal energies.